The present invention relates to an improved method for the preparation of water-insoluble carboxymethyl cellulose (CMC) absorbents.
The use of CMC as an absorbent material in catamenial devices or other absorbent dressings has been known in the literature for a number of years. See, for example, Masci et al U.S. Pat. Nos. 2,764,159 and 2,772,999 granted on Sept. 25 and Dec. 4, 1956, respectively; Ashton et al U.S. Pat. No. 2,766,137 granted Oct. 9, 1956; Graham U.S. Pat. No. 3,005,456 granted Oct. 24, 1961; Burgeni et al U.S. Pat. No. 3,067,745 granted Dec. 11, 1962; and Lewing U.S. Pat. No. 3,371,666 granted Mar. 5, 1968.
Graham disclosed that only CMC's having a DS value (the number of carboxymethyl groups per anhydroglucose unit in the cellulose chain) less than about 0.35 are useful as absorbents, and described those materials having higher DS values as too soluble for such purpose. It has, however, subsequently been disclosed that CMC's having higher DS values are also suitable for use in absorbent dressings, particularly if insolubilized, e.g., by cross-linking. In this connection reference may be made, for example, to the aforesaid Ashton et al and Masci et al patents; Elliot U.S. Pat. No. 2,639,239 granted May 19, 1953; Dean et al U.S. Pat. No. 3,589,364 granted June 29, 1971; Ells et al U.S. Pat. No. 3,618,607, granted Nov. 9, 1971; Schoggen U.S. Pat. No. 3,678,031, granted July 18, 1972; Chatterjee U.S. Pat. No. 3,731,686, granted May 8, 1973; and Kaczmarzyk et al U.S. Pat. No. 4,044,766, granted Aug. 30, 1977. One commonly used procedure which has been proposed for preparing water-insoluble CMC's involves insolubilizing the material merely by heat-catalyzed cross-linking. See, for example, the aforesaid Chatterjee patent, and Reid U.S. Pat. No. 3,379,720 granted Apr. 23, 1968.
Material thus insolubilized may be in the salt form, or the carboxylate moieties thereof may be partially acidified and the polymer thus placed in the so-called "acid form". Insolubilized CMC's in both the salt (see, for example, the aforesaid Chatterjee and Kaczmarzyk patents) and acid forms (see, for example, the aforesaid Ashton et al and Masci et al patents) have been described as suitable for use as absorbents for dressing materials.
Copending application Ser. No. 906,724 entitled, "Preparation of Water-Insoluble Carboxymethyl Cellulose Absorbents", in the names of Herman Marder, Nathan Field and Makoto Shinohara describes an improved process for the preparation of acid-form CMC's suitable for application as absorbents. The present invention, on the other hand, is directed to an improved technique for the production of CMC salt absorbents.
It is, accordingly, a principal object of the present invention to provide an improved process for the preparation of water-insoluble CMC materials in the salt form, the products of which may be readily utilized as absorbents for catamenial devices and other absorbent dressings.
Other objects and advantages of the process of the invention will be apparent from the following description of preferred embodiments thereof, considered in connection with the annexed graphical drawing illustrating the reaction temperatures and times necessary for insolubilizing CMC salts employing the process of the invention.